For many years, It has been well understood that the performance of an antenna diminishes as its dimension, as a fraction of the electrical wavelength, falls significantly below λ/2. The ‘Q’ of an electrically short antenna is inversely proportional to the cube of its electrical length. For electrically short antennas particularly, this high ‘Q’ limits the possible modulation bandwidth.
While it is possible, with passive components, to match a narrow-band antenna to a single (carrier) frequency, the impedance mismatch presented to the modulation sideband frequencies has the effect of attenuating them, while causing electrical stress to the power amplifier in these mis-match conditions.
Another prior art technique is described in a publication by Blinchikoff and Zverev which explained a means to broadband an antenna using passive, filter synthesis strategies. While effective in extending usable bandwidth, that system is still ultimately bound by the Bode-Fano limit.
Also broadbanding strategies using Non-Foster circuits have been applied in receive circuits. Using such amplifier circuitry to synthesize negative capacitive and inductive elements, the Bode-Fano limit can be effectively circumvented. However, because of the limited dynamic range and electrical inefficiency of the Non-Foster circuit elements, these approaches are often impractical in transmit applications.
Consequently, there exists a need for improved methods and systems for efficiently transmitting with electrically short antennae.